An S RNase gene of Lycopersicon peruvianum L. is highly expressed in transgenic tobacco but does not affect self-incompatibility

Lycopersicon peruvianum has a gametophytic self-incompatibility (GSI) mechanism controlled by a single genetic locus (S locus) with multiple alleles. S RNases, an allelic series of abundant stylar proteins, are products of the S locus in L. peruvianum and other Solanaceous plants. We introduced a genomic clone for the S₁₁ RNase from L. peruvianum into a self-compatible species (Nicotiana tabacum) to examine if the expression pattern in the heterologous plant mimics that in L. peruvianum. The resultant transgenic N. tabacum plants expressed the introduced gene at a high level in their styles, similar to the S₁₁ gene expression in L. peruvianum. The S₁₁ RNase gene was expressed in the style at a similar stage of flower development in both the transgenic tobacco plants and L. peruvianum, suggesting that the regulatory mechanism for S RNase gene expression is operating in a self-compatible heterologous plant. However, the transgenic plants did not show any morphological changes or altered pollination behaviour as a result of this expression. Unexpectedly, the S₁₁ RNase transcript was also found in developing anthers and mature pollen of the transgenic plants although the expression level is much lower compared to that in stylar tissues. This expression pattern has not been observed in L. peruvianum.